U.S. patent application number 12/098155 was filed with the patent office on 2008-10-23 for hydroxyalkyl methylcellulose having solubility and thermoreversible gelation properties improved.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Kazuhisa HAYAKAWA, Rumiko ITOH.
Application Number | 20080262216 12/098155 |
Document ID | / |
Family ID | 39591553 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080262216 |
Kind Code |
A1 |
HAYAKAWA; Kazuhisa ; et
al. |
October 23, 2008 |
HYDROXYALKYL METHYLCELLULOSE HAVING SOLUBILITY AND THERMOREVERSIBLE
GELATION PROPERTIES IMPROVED
Abstract
Provided is hydroxyalkyl methylcellulose which can be dissolved
at room temperature of 20 to 30.degree. C. and has high
thermoreversible gel strength during thermoreversible gelation.
More specifically, provided is water-soluble hydroxyalkyl
methylcellulose having a molar substitution of hydroxyalkoxyl
groups of 0.05 to 0.1 and a substitution degree of methoxyl groups
of 1.6 to 1.9, wherein the hydroxyalkoxyl groups are classified
into substituted hydroxyalkoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups substituted further with methoxyl groups and
unsubstituted hydroxyalkoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups not further substituted; and a ratio (A/B) of
a molar fraction (A) of the substituted hydroxyalkoxyl groups to a
molar fraction (B) of unsubstituted hydroxyalkoxyl groups is 0.4 or
greater.
Inventors: |
HAYAKAWA; Kazuhisa;
(Joetsu-shi, JP) ; ITOH; Rumiko; (Joetsu-shi,
JP) |
Correspondence
Address: |
ROBERTS MLOTKOWSKI SAFRAN & COLE, P.C.;Intellectual Property Department
P.O. Box 10064
MCLEAN
VA
22102-8064
US
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
39591553 |
Appl. No.: |
12/098155 |
Filed: |
April 4, 2008 |
Current U.S.
Class: |
536/95 |
Current CPC
Class: |
C08B 11/193
20130101 |
Class at
Publication: |
536/95 |
International
Class: |
C08B 11/08 20060101
C08B011/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2007 |
JP |
2007-111546 |
Claims
1. Water-soluble hydroxyalkyl methylcellulose having a molar
substitution of hydroxyalkoxyl groups of 0.05 to 0.1 and a
substitution degree of methoxyl groups of 1.6 to 1.9, wherein the
hydroxyalkoxyl groups are classified into substituted
hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups substituted further with methoxyl groups and unsubstituted
hydroxylakoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups not further substituted; and a ratio (A/B) of a molar
fraction (A) of the substituted hydroxyalkoxyl groups to a molar
fraction (B) of the unsubstituted hydroxyalkoxyl groups is 0.4 or
greater.
2. The water-soluble hydroxyalkyl methylcellulose according to
claim 1, wherein said hydroxyalkoxyl groups are hydroxypropoxyl
groups or hydroxyethoxyl groups.
3. A method for preparing water-soluble hydroxyalkyl
methylcellulose, comprising steps of: reacting cellulose and an
alkali to obtain alkali cellulose; and reacting the alkali
cellulose with a hydroxyalkyl etherification agent and a methyl
etherification agent to obtain a water-soluble hydroxyalkyl
methylcellulose having a molar substitution of hydroxyalkoxyl
groups of 0.05 to 0.1 and a substitution degree of methoxyl groups
of 1.6 to 1.9, the hydroxyalkoxyl groups being classified into
substituted hydroxyalkoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups substituted further with methoxyl groups and
unsubstituted hydroxyalkoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups not further substituted and a ratio (A/B) of
a molar fraction (A) of the substituted hydroxyalkoxyl groups to a
molar fraction (B) of the unsubstituted hydroxyalkoxyl groups being
0.4 or greater; wherein the step for obtaining the water-soluble
hydroxyalkyl methylcellulose comprises a stage of adding the
hydroxyalkyl etherification agent and a stage of adding the methyl
etherification agent after the reaction between the hydroxylalkyl
etherification agent and the alkali cellulose; or a stage of adding
the hydroxyalkyl etherification agent and the methyl etherification
agent so that 40% by weight or greater of a stoichiometric amount
of the methyl etherification agent remains unreacted upon
completion of the reaction of 60% by weight or greater of a
stoichiometric amount of the hydroxyalkyl etherification agent.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to hydroxyalkyl
methylcelluloses having excellent thermoreversible gel strength and
improved solubility.
[0003] 2. Description of the Related Art
[0004] In hydroxypropyl methylcellulose obtained by
ether-substitution of methyl groups and hydroxypropyl groups to
cellulose, methoxyl groups are localized in the molecule relative
to the cellulose chain. Hydroxypropyl methylcellulose has therefore
"thermoreversible gelation properties". Described specifically,
when an aqueous solution of hydroxypropyl methylcellulose is
heated, hydrophobic hydration of the methoxyl groups localized in
the molecule occurs and it turns into a hydrous gel. When the
resulting gel is cooled, on the other hand, hydrophobic hydration
decreases, whereby the gel returns to the original aqueous
solution. Because of such thermoreversible gelation properties, the
aqueous solution shows excellent shape retention even after
heating. For example, when hydroxyalkyl methylcellulose is used as
a binder for extrusion of ceramics, the hydroxyalkyl
methylcellulose dissolved in water is mixed, kneaded with ceramic
particles, formed into a certain shape, and dried with heating
wherein the hydroxyalkyl methylcellulose turns into a gel by
heating. When the gelled portion has high strength, defects such as
cracks caused by shrinkage strain during drying can be prevented.
Hydroxyalkyl methylcelluloses are therefore used exclusively as a
binder for extrusion of ceramics.
[0005] Methylcellulose having no hydroxyalkoxyl groups has
excellent thermoreversible gelation performance. The
thermoreversible gel strength of the methylcellulose is determined
by placing a 2.5% by weight aqueous solution of it in a constant
temperature bath of 80.degree. C. so as to cause thermoreversible
gelation after 15 minutes; inserting a cylindrical rod having a
diameter of 15 mm downward into the gel at a rate of 5 cm/min; and
measuring a maximum load (g) applied to the cylindrical rod when it
is inserted into 2 cm inside of the gel. The thermoreversible gel
strength is obtained by dividing the maximum load (g) by the
cross-sectional area of the rod. The thermoreversible gel strength
thus determined is as high as from 500 to 700 g/cm.sup.2. When such
methylcellulose is used for extrusion of ceramic particles,
followed by drying with heating, cracks due to shrinkage strain
during drying can be minimized. Even if the amount of
methylcellulose added to the ceramic is reduced, defects caused by
cracks during drying can be reduced.
[0006] When a molar substitution of hydroxyalkoxyl groups of more
than 0.1 is introduced into methylcellulose, the resulting
hydroxyalkyl methylcellulose has thermoreversible gel strength of
100 g/cm.sup.2 or less. For example, hydroxypropyl methylcellulose
having a molar substitution of hydroxypropoxyl groups of 0.15 and a
substitution degree of methoxyl groups of 1.8 renders
thermoreversible gel strength of 30 g/cm.sup.2. Hydroxyethyl
methylcellulose having a molar substitution of hydroxyethoxyl
groups of 0.15 and a substitution degree of methoxyl groups of 1.8
renders thermoreversible gel strength of 25 g/cm.sup.2. This means
that when high thermoreversible gel strength is required,
methylcellulose having no hydroxyalkoxyl groups introduced is
preferred. In order to dissolve methylcellulose having no
hydroxyalkoxyl groups introduced in water, however, a water
temperature has to be adjusted to 10.degree. C. or less.
Methylcellulose insoluble in water cannot render its original
thermoreversible gel strength and therefore becomes practically
useless. It is therefore difficult to use methylcellulose having no
hydroxyalkoxyl groups introduced.
[0007] Japanese Patent Application Examined Publication No.
62-059074/1987 discloses that hydroxyalkyl methylcelluloses having
a molar substitution of hydroxyalkoxyl groups of 0.02 to 0.13 can
dissolve in water after a predetermined time even when the
temperature is set at approximately 30.degree. C., indicating that
dissolution is possible without the dissolution temperature
decreased. Further, Japanese Patent Application Examined
Publication No. 62-059074/1987 discloses that the thermoreversible
gelation temperature of methylcellulose can be raised by
introduction of hydroxyalkoxyl groups therein.
SUMMARY OF THE INVENTION
[0008] Japanese Patent Application Examined Publication No.
62-059074/1987 discloses that methylcellulose having hydroxyalkoxyl
groups introduced can have a higher thermoreversible gelation
temperature than that of the methylcellulose having no
hydroxyalkoxyl groups, but does not disclose whether the high
thermoreversible gelation strength can be maintained or not. The
present inventors have found that the hydroxyalkyl methylcellulose
described by Japanese Patent Application Examined Publication No.
62-059074/1987 does not always have necessary thermoreversible
gelation strength. Accordingly, there is a demand for the
development of hydroxyalkyl methylcellulose such as hydroxypropyl
methylcellulose and hydroxyethyl methylcellulose which can dissolve
easily even without the temperature lowered to 10.degree. C. or
less and which has higher strength of thermoreversible gel which is
produced by heating the solution of hydroxyalkyl
methylcellulose.
[0009] With the foregoing in view, the present invention has been
made. An object of the present invention is to provide hydroxyalkyl
methylcellulose which can be dissolved at a room temperature of 20
to 30.degree. C. and have high thermoreversible gel strength when
it becomes thermoreversible gel.
[0010] With a view to accomplishing the above-described object, the
present inventors have carried out an intensive investigation. As a
result, it has been found that water-soluble hydroxylalkyl
methylcellulose having a molar substitution of hydroxyalkoxyl
groups of from 0.05 to 0.1, a substitution degree of methoxyl
groups of from 1.6 to 1.9, and a ratio of (A/B) of 0.4 or greater
wherein (A) is a molar fraction of substituted hydroxyalkoxyl
groups having hydroxyl groups of hydroxyalkoxyl groups substituted
further with methoxyl groups and (B) is a molar fraction of
unsubstituted hydroxylakoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups not substituted further with methoxyl groups,
can dissolve at a room temperature of from 20 to 30.degree. C. and
have thermoreversible gel strength comparable to that of
methylcellulose having no hydroxyalkoxyl groups introduced and
sufficiently higher than that of commercially available
hydroxypropyl methylcellulose or hydroxyethyl methylcellulose,
leading to the completion of the present invention.
[0011] According to the present invention, there is provided
water-soluble hydroxyalkyl methylcellulose having a molar
substitution of hydroxyalkoxyl groups of from 0.05 to 0.1 and a
substitution degree of methoxyl groups of from 1.6 to 1.9, wherein
the hydroxyalkoxyl groups are classified into substituted
hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups substituted further with methoxyl groups and unsubstituted
hydroxylakoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups not further substituted and a ratio (A/B) of a molar
fraction (A) of the substituted hydroxyalkoxyl groups to a molar
fraction (B) of the unsubstituted hydroxyalkoxyl groups is 0.4 or
greater.
[0012] According to the present invention, there is also provided a
method for preparing water-soluble hydroxyalkyl methylcellulose,
comprising steps of:
[0013] reacting cellulose and an alkali to obtain an alkali
cellulose; and
[0014] reacting the alkali cellulose with a hydroxyalkyl
etherification agent and a methyl etherification agent to obtain a
water-soluble hydroxyalkyl methylcellulose having a molar
substitution of hydroxyalkoxyl of from 0.05 to 0.1 and a
substitution degree of methoxyl of from 1.6 to 1.9, the
hydroxyalkoxyl groups being classified into substituted
hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups substituted further with methoxyl groups and unsubstituted
hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups not further substituted and a ratio (A/B) of a molar
fraction (A) of the substituted hydroxyalkoxyl groups to a molar
fraction (B) of the unsubstituted hydroxyalkoxyl groups being 0.4
or greater, wherein
[0015] the step for obtaining the water-soluble hydroxyalkyl
methylcellulose comprises a stage of adding the hydroxyalkyl
etherification agent and a stage of adding the methyl
etherification agent after the reaction between the hydroxylalkyl
etherification agent and the alkali cellulose; or a stage of adding
the hydroxyalkyl etherification agent and the methyl etherification
agent so that 40% by weight or greater of a stoichiometric amount
of the methyl etherification agent remains unreacted upon
completion of the reaction of 60% by weight or greater of a
stoichiometric amount of the hydroxyalkyl etherification agent.
[0016] According to the present invention, provided is a
water-soluble hydroxyalkyl methylcellulose which can dissolve at a
room temperature of from 20 to 30.degree. C. and have high
thermoreversible gel strength when it becomes a thermoreversible
gel.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] The present invention will hereinafter be described
specifically.
[0018] Although no particular limitation is imposed on the
water-soluble hydroxyalkyl methylcellulose to be used in the
present invention having a molar substitution of hydroxyalkoxyl
groups of 0.05 to 0.1 and a substitution degree of methoxyl groups
of 1.6 to 1.9, it may be prepared by impregnating cellulose with a
predetermined amount of an aqueous alkali solution as presented in
Japanese Patent Application Unexamined Publication No. 2001-302701,
and then reacting the resulting alkali cellulose with necessary
amounts of a methyl etherification agent (preferably methyl
chloride) and a hydroxyalkyl etherification agent (preferably
propylene oxide or ethylene oxide).
[0019] The term "a molar substitution of hydroxyalkoxyl groups" as
used herein means an average mole of hydroxyalkoxyl groups
(preferably hydroxypropoxyl groups or hydroxyethoxyl groups) added
per glucose ring unit of cellulose. The term "a substitution degree
of methoxyl groups" means the average number of hydroxyl groups
substituted with methoxyl groups per glucose ring unit of the
cellulose.
[0020] In order to adjust a ratio (A/B) of a molar fraction (A) of
substituted hydroxyalkoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups substituted further with methoxyl groups to a
molar fraction (B) of unsubstituted hydroxyalkoxyl groups having
hydroxyl groups of hydroxyalkoxyl groups not substituted further
with methoxyl groups to be 0.4 or greater, an addition order or
rate of etherification agents can be controlled to perform
substitution of many hydroxyalkoxyl groups prior to substitution of
methoxyl groups
[0021] More specifically, after cellulose is reacted with a
necessary amount of an alkali (preferably, a solution of caustic
soda) to prepare the corresponding alkali cellulose, a hydroxyalkyl
etherification agent (for example, propylene oxide or ethylene
oxide) is added to perform an etherification reaction preferably at
from 50 to 95.degree. C. A methyl etherification agent (for
example, methyl chloride) is then added to perform a subsequent
reaction.
[0022] Alternatively, a hydroxyalkyl etherification agent (for
example, propylene oxide or ethylene oxide) and a methyl
etherification agent (for example, methyl chloride) are added
successively or as needed so that even upon completion of the
reaction of preferably 60% by weight or greater, more preferably
70% by weight or greater, still more preferably 80% by weight or
greater of a stoichiometric amount of the hydroxyalkyl
etherification agent, preferably 40% by weight or greater, more
preferably 50% by weight or greater, still more preferably 60% by
weight or greater of a stoichiometric amount of methyl chloride
remains unreacted. More specifically, although the hydroxyalkyl
etherification agent and the methyl etherification agent may be
added simultaneously or successively in any order, a ratio of
addition time of the methyl etherification agent to that of the
hydroxyalkyl etherification agent may fall within a range of
preferably from 1.3 to 3, especially preferably from 1.5 to 3.
[0023] According to the present invention, the water-soluble
hydroxyalkyl methylcellulose may be preferably hydroxypropyl
methylcellulose or hydroxyethyl methylcellulose. In other words,
the hydroxyalkoxyl group introduced by the hydroxyalkyl
etherification agent may be preferably a hydroxypropoxyl group or a
hydroxyethoxyl group.
[0024] The molar substitution of hydroxypropoxyl groups and a
substitution degree of methoxyl groups of the hydroxyalkyl
methylcellulose of the present invention can be measured in
accordance with the analysis method of substitution degree of
hypromellose (hydroxypropyl methylcellulose) as described in the
Japanese Pharmacopoeia, Fifteenth Edition or "Standard Method of
Testing HYDROXYPROPYL METHYLCELLULOSE" specified in ASTM
D-2363-72/USA. The molar substitution and the substitution degree
can also be analyzed by NMR or infrared absorption analysis.
[0025] The substitution degree of methoxyl groups of hydroxyethyl
methylcellulose can be measured by the analysis method of
methylcellulose as specified in The Japanese Pharmacopoeia
Fifteenth Edition or "Standard Test Method for Methylcellulose" as
specified in ASTM D-1347-72/USA, as well as the method described in
J. G. Cobler, et al., "Determination of Alkoxyl Substitution Ether
by Gas Chromatography" or in Talanta, Vol. 9, 473-481 (1962). The
molar substitution of hydroxyethoxyl can be measured in accordance
with Ying-ChiLee, et al., "Determination of Molar Substitution
Ratio of Hydroxyethyl Starches by Gas Chromatography", Anal. Chem.
55, 332-338 (1983), or "Standard Test Method for
Hydroxyethylcellulose" as specified in ASTM D2364-75/USA.
[0026] In addition to the above-described analysis methods of the
molar substitution or the substitution degree, another method such
as H-NMR or .sup.13C-NMR may be employed for the measurement.
[0027] When substitution of methoxyl groups follows substitution of
hydroxyalkoxyl groups such as hydroxypropoxyl groups or
hydroxyethoxyl groups, the hydroxyl groups of these hydroxyalkoxyl
groups can be substituted further with the methoxyl groups. When
the hydroxyl groups of the cellulose are substituted with methoxyl
groups, on the other hand, the methoxy groups are not substituted
further with hydroxyalkoxyl groups at the substitution site of the
methoxyl groups because the methoxyl groups have no hydroxyl
groups.
[0028] If total moles of methoxyl groups, unsubstituted
hydroxyalkoxyl groups, substituted hydroxyalkoxyl groups, and
substituents (OH) substituted with neither methoxyl groups nor
hydroxyalkyl groups can be determined and a molar substitution of
the substituted hydroxyalkoxyl groups having hydroxyl groups of
hydroxyalkoxyl groups substituted further with methoxyl groups, can
be determined separately, a substitution molar fraction of
substituted hydroxyalkoxyl groups can be calculated by dividing the
molar substitution of the substituted hydroxyalkoxyl groups by the
total moles.
[0029] If the molar substitution of unsubstituted hydroxyalkoxyl
groups having hydroxyl groups of hydroxyalkoxyl groups not
substituted with methoxyl groups is able to be determined, a
substitution molar fraction of the unsubstituted hydroxyalkoxyl
groups can be calculated by dividing the molar substitution of the
unsubstituted hydroxyalkoxyl groups by the total moles.
[0030] Examples of the method for analyzing a water-soluble
hydroxyalkyl methylcellulose to find that it is has a ratio (A/B)
of 0.4 or greater wherein (A) is a molar fraction of substituted
hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl
groups substituted further with methoxyl groups and (B) is a molar
fraction of unsubstituted hydroxyalkoxyl groups having hydroxyl
groups of hydroxyalkoxyl groups not substituted further with
methoxyl groups include, as described in Macromolecules, 20, 2413
(1987) or Journal of Society of Textile and Cellulose Industry
Japan, 40, T-504 (1984), a method comprising steps of hydrolyzing
cellulose ether in sulfuric acid, neutralizing, filtering,
purifying, acetylating the purified product, subjecting the
acetylated product to .sup.13C-NMR, liquid chromatography or gas
chromatography and determining based on the characteristics of each
detection graph identified by using a mass analyzer.
[0031] A weight average polymerization degree of the hydroxyalkyl
methylcellulose thus obtained can be determined by measuring a
weight average molecular weight by using a combination of gel
permeation chromatography and light scattering method in accordance
with a molecular weight measuring method as described in Journal of
Polymer Science and Technology, 39(4), 293-298 (1982) and dividing
the weight average molecular weight by a molecular weight per unit
hydroxypropylmethylcellulose molecule. The kind or conditions of
the solvent, temperature, column, or wavelength of the light
scattering apparatus employed in the measurement of the weight
average molecular weight are not limited to those described in the
Journal of Polymer Science and Technology but can be selected as
needed. The weight average molecular weight can also be determined
by ultracentrifugation or conversion from a viscosity average
molecular weight.
[0032] Hydroxyalkyl methylcellulose having a higher weight average
polymerization degree tends to exhibit higher thermoreversible gel
strength when it is in the form of aqueous solutions having the
same concentration. Even hydroxyalkyl methylcellulose having a low
weight average polymerization degree can have necessary strength by
adjustment of the concentration of the aqueous solution. When it is
used as a binder, a weight average polymerization degree which can
provide high thermoreversible gel strength even if it is added in a
small amount may be preferably from 100 to 10000. When the weight
average polymerization degree is smaller than 100, sufficient
thermoreversible gel strength may not be obtained for use as an
additive and an amount to be added may exceed 10% by weight. When
the weight average polymerization degree is higher than 10000, the
preparation of the hydroxyalky methylcellulose may become difficult
in practice because raw material cellulose having a certain
polymerization degree have to be selected or prepared.
[0033] The cellulose (pulp) to be used for the preparation of the
hydroxyalkyl methylcellulose of the present invention may include
wood pulp obtained by refining the wood and cotton pulp (linter
pulp) obtained from cotton fibers.
[0034] The dissolution temperature of the hydroxypropyl
methylcellulose may be measured in the following manner.
[0035] Hydroxypropyl methylcellulose powder and hot water are
placed in a 300-ml beaker so as to prepare an 1 by weight aqueous
solution of the hydroxypropyl methylcellulose. The resulting
solution is cooled while stirring at 400 rpm. Viscosities of the
aqueous solution are measured at predetermined temperatures of the
aqueous solution. The temperature at which the slope of a line
connecting the viscosities plotted against temperatures starts to
blunt is measured as the dissolution temperature
[0036] The thermoreversible gel strength may be determined in the
following manner. A 2% by weight aqueous solution of hydroxypropyl
methylcellulose is prepared, added into a 50-ml beaker and heated
in a bath of 80.degree. C. for 30 minutes to form a
thermoreversible gel. The maximum force applied to a cylindrical
rod having a diameter of 15 mm when the cylindrical rod is inserted
by 2 cm downward into the gel at a rate of 5 cm/min is measured
using a rheometer manufactured by Rheotec Co., Ltd. The
thermoreversible gel strength is calculated by dividing the maximum
force value by a cross-sectional area of the cylindrical rod.
EXAMPLES
[0037] The present invention will hereinafter be described more
specifically by Examples and Comparative Examples. However, it
should not be construed that the present invention is limited to or
by these Examples.
Example 1
[0038] Wood-derived high-purity dissolving pulp manufactured by
Nippon Paper Industries Co., Ltd. was pulverized with a roller
mill, sifted through a 600 .mu.m sieve and fed at a constant rate
of 10 g/min to a twin-screw kneader "Sl KRC Kneader" (trade name;
product by Kurimoto, Ltd., having a paddle diameter of 25 mm, an
outer diameter of 255 mm, L/D=10.2, an inner volume of 0.12 liter
and a rotation speed of 100 rpm). At the same time, a 49% by weight
sodium hydroxide solution was fed at a constant rate of 21.5 g/min
from an inlet provided at a pulp feed opening to add the aqueous
alkali solution to the cellulose. Of the alkali cellulose obtained
by continuous operation for about 30 minutes, a 585.0 g portion was
placed in an autoclave equipped with a Ploughshare type internal
agitating blade. After the pressure was reduced to -97 kPa,
nitrogen was added into the autoclave to reach an atmospheric
pressure. The pressure was then reduced again to -97 kPa. The 20 g
of propylene oxide and 253.9 g of methyl chloride were added via a
pressure pump while setting a ratio of addition times of methyl
chloride to propylene oxide at 3 (60 minutes of methyl chloride
addition time to 20 minutes of propylene oxide) and fishing the
addition of propylene oxide prior to the addition of methyl
chloride. They were reacted for 2 hours at an internal temperature
of 60.degree. C. The temperature was then raised to 90.degree. C.
over 30 minutes and kept at 90.degree. C. for 30 minutes, whereby
an etherification reaction was completed.
[0039] The reaction product was washed with hot water of 85.degree.
C. or greater and dried in a small Willey mill. It was analyzed in
accordance with the analysis method of the substitution degree of
hypromellose (hydroxypropyl methylcellulose) described in the
Japanese Pharmacopoeia, Fifteenth Edition. As a result of the
analysis, the hydroxypropyl methylcellulose thus obtained had a
molar substitution of hydroxypropoxyl groups of 0.07 and a
substitution degree of methoxyl groups of 1.8. The molecular weight
of the hydroxypropyl methylcellulose thus obtained was determined
in accordance with the molecular weight measuring method as
described in Japanese Journal of Polymer Science and Technology,
39(4), 293-298 (1982) and a weight average polymerization degree
was calculated to be 1200.
[0040] After adding 2 ml of a 3% by weight aqueous sulfuric acid
solution to 50 mg of the resulting hydroxypropylmethylcellulose and
hydrolyzing the resulting mixture at 140.degree. C. for 3 hours,
the hydrolysate was neutralized with about 0.7 g of barium
carbonate. To the neutralized hydrolysate was added 3 ml of
methanol to dissolve and disperse the former in the latter, and the
resulting solution was then centrifuged at 500 G. The supernatant
was filtered through a filter having 0.45 .mu.m openings. Reduction
of the glucose ring was performed at 37 to 38.degree. C. for 1 hour
by adding 120 .mu.l of a solution obtained by dissolving 1.5 g of
NaBH.sub.4 in 10 ml of a 0.2 N aqueous NaOH solution. After
addition of 100 .mu.l of acetic acid thereto, the solvent was
evaporated. By adding 2 ml of pyridine and 1 ml of acetic
anhydride, the acetylation was carried out at 120.degree. C. for 3
hours. The resulting product (1 .mu.l) was passed through DB-5
Column (trade name; product of J & W) heated to 150 to
220.degree. C. and a retention time of each decomposed component
was measured using an FID detector.
[0041] A ratio (A/B) of a molar fraction (A) of substituted
hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl
groups substituted further with methoxyl groups to a molar fraction
(B) of unsubstituted hydroxypropoxyl groups having hydroxyl groups
of hydroxypropoxyl groups not substituted further with methoxyl
groups was determined based on the ratio of areas of the peaks at
which the structures of decomposed components had been identified
in advance by a mass analyzer. The ratio (A/B) was 0.8.
[0042] The obtained hydroxypropyl methylcellulose powder and hot
water were placed in a 300-ml beaker in order to prepare a 1% by
weight aqueous solution of the hydroxypropylmethylcellulose. The
resulting solution was cooled at a rate of 2.degree. C. per 10
minutes while stirring at 400 rpm. The viscosity of the aqueous
solution was measured relative to the temperature of the aqueous
solution, and the dissolution temperature at which the slope of a
line connecting the viscosities plotted against the temperature
started to blunt was measured. The dissolution temperature was
25.degree. C.
[0043] A 2% by weight aqueous solution of the resulting
hydroxypropyl methylcellulose was prepared and placed in a 50 ml
beaker. Thermoreversible gelation of the aqueous solution was then
conducted for 30 minutes in a bath of 80.degree. C.
Thermoreversible gelation strength was determined by measuring,
with a rheometer manufactured by Rheotec Co., Inc., a force applied
to a cylindrical rod having a diameter of 15 mm when the rod was
inserted downward into the gel by 2 cm at a rate of 5 cm/min, and
dividing the force value by a cross-sectional area of the rod. The
thermoreversible gelation strength was 150 g/cm.sup.2.
Examples 2 to 4 and Comparative Examples 1 to 3
[0044] Hydroxypropyl methylcellulose was prepared in each of
Examples 2 to 4 and Comparative Examples 1 to 3 in the same manner
as in Example 1 except for the change of the kind of pulp, added
amounts of methyl chloride and propylene oxide, and an addition
time ratio of methyl chloride addition time to propylene oxide
addition time as shown in Table 1. Using the obtained hydroxypropyl
methyl cellulose, a substitution degree of methoxyl groups, a molar
substitution of hydroxypropoxyl groups, a ratio (A/B) of a molar
fraction (A) of substituted hydroxypropoxyl groups having hydroxyl
groups of hydroxypropoxyl groups substituted further with methoxyl
groups to a molar fraction (B) of unsubstituted hydroxypropoxyl
groups having hydroxyl groups of hydroxypropoxyl groups not
substituted further with methoxyl groups, a weight average
polymerization degree, a dissolution temperature and a
thermoreversible gel strength were determined in the same manner as
in Example 1 as shown in Table 1.
TABLE-US-00001 TABLE 1 methyl propylene molar chloride oxide
addition substitution substitution weight thermoreversible (MC)
(PO) time degree of of average dissolution gel type of added added
ratio of methoxyl hydroxypropoxyl plolymerization temperature
strength pulp (g) (g) MC/PO group group A/B*.sup.1 degree (.degree.
C.) (g/cm.sup.2) Example 1 wood pulp 254 20 3 1.8 0.07 0.8 1200 25
150 Example 2 cotton pulp 200 18 2.8 1.6 0.05 0.7 10000 20 200
Example 3 wood pulp 206.9 40 1.5 1.9 0.07 0.6 500 27 120 Example 4
wood pulp 220 20 1.3 1.7 0.07 0.4 1200 20 100 Comp. wood pulp 254
50 1 1.8 0.15 0.4 1200 35 30 Ex. 1 Comp. wood pulp 220 80 1.2 1.7
0.25 0.5 1200 43 5 Ex. 2 Comp. wood pulp 220 5 1.5 1.9 0.04 0.6
1200 12 150 Ex. 3 *.sup.1A ratio (A/B) of a molar fraction (A) of
substituted hydroxypropoxyl groups having hydroxyl groups of
hydroxypropoxyl groups substituted further with methoxyl groups to
a molar fraction (B) of unsubstituted hydroxypropoxyl groups having
hydroxyl groups of hydroxypropoxyl groups not substituted further
with methoxyl groups.
Example 5
[0045] Of the alkali cellulose obtained in Example 1, a 585.0 g
portion was placed in an autoclave equipped with a Ploughshare type
internal agitating blade. After the pressure was reduced to -97
kPa, nitrogen was added into the autoclave to reach an atmospheric
pressure. The pressure was then reduced again to -97 kPa. The 20 g
of propylene oxide was added to the autoclave via a pressure pump
and reacted for two hours at the internal temperature controlled to
60.degree. C. Subsequently, 253.9 g of methyl chloride were added
to the autoclave which had been cooled to 20.degree. C. The
temperature of the autoclave was then raised to 90.degree. C. over
30 minutes and kept at 90.degree. C. for 30 minutes, whereby an
etherification reaction was completed. Hydroxypropyl
methylcellulose having a weight average polymerization degree of
1000, a substitution degree of methoxyl groups of 1.8 and a molar
substitution of hydroxypropoxyl groups of 0.09 was obtained.
[0046] A ratio (A/B) of a molar fraction (A) of substituted
hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl
groups substituted further with methoxyl groups to a molar fraction
(B) of unsubstituted hydroxyproxyl groups having hydroxyl groups of
hydroxyproxyl groups not substituted further with methoxyl groups
was found to be 0.9. The dissolution temperature and the
thermoreversible gel strength of the resulting hydroxypropyl
methylcellulose measured in the same manner as in Example 1 were
25.degree. C. and 160 g/cm.sup.2, respectively.
Examples 6 to 9 and Comparative Examples 4 to 6
[0047] In the same manner as in Example 1 except that the reaction
took place for 2 hours at an internal temperature controlled to
55.degree. C. while adding ethylene oxide in amounts shown in Table
2 instead of adding propylene oxide used in Examples 1 to 4 and
Comparative Examples 1 to 3, hydroxyethyl methylcellulose shown in
Table 2 was prepared in place of hydroxypropyl methylcellulose
prepared in Examples 1 to 4 and Comparative Examples 1 to 3.
[0048] With regards to the hydroxyethyl methylcelluloses thus
obtained, a ratio (A/B) of a molar fraction (A) of substituted
hydroxyethoxyl groups having hydroxyl groups of hydroxyethoxyl
groups substituted further with methoxyl groups to a molar fraction
(B) of unsubstituted hydroxyethoxyl groups having hydroxyl groups
of hydroxyethoxyl groups not substituted further with methoxyl
groups, a weight average polymerization degree, a dissolution
temperature and a thermoreversible gel strength were measured in
the same manner as in Examples 1 to 4 and Comparative Examples 1 to
3. The results are shown in Table 2. The substitution degree of
methoxyl groups and the molar substitution of hydroxyethoxyl groups
were measured and calculated in accordance with ASTM D1347-72/USA
and ASTM D2364-75/USA, respectively. The results are shown in Table
2.
TABLE-US-00002 TABLE 2 methyl ethylene molar chloride oxide
addition substitution substitution weight thermoreversible (MC)
(EO) time degree of of average dissolution gel type of added added
ratio of methoxyl hydroxyethoxyl plolymerization temperature
strength pulp (g) (g) MC/EO group group A/B*.sup.1 degree (.degree.
C.) (g/cm.sup.2) Example 6 wood pulp 256 8 3 1.8 0.07 0.8 1100 27
145 Example 7 cotton pulp 190 6 1.8 1.7 0.05 0.7 12000 21 190
Example 8 wood pulp 265 11 1.5 1.9 0.1 0.6 400 30 100 Example 9
wood pulp 256 8 1.3 1.6 0.07 0.4 1300 22 90 Comp. Ex. 4 wood pulp
256 16 1 1.8 0.15 0.4 1100 37 15 Comp. Ex. 5 wood pulp 256 27 1.2
1.7 0.25 0.5 1100 45 8 Comp. Ex. 6 wood pulp 256 2 1.5 1.6 0.02 0.6
1300 14 140 *.sup.1A ratio (A/B) of a molar fraction (A) of
substituted hydroxyethoxyl groups having hydroxyl groups of
hydroxyethoxyl groups substituted further with methoxyl groups to a
molar fraction (B) of unsubstituted hydroxyethoxyl groups having
hydroxyl groups of hydroxyethoxyl groups not substituted further
with methoxyl groups.
Example 10
[0049] In the same manner as in Example 5 except that in the
reaction of Example 5, ethylene oxide was added instead of
propylene oxide in an autoclave and reacted for 2 hours at the
internal temperature controlled to 55.degree. C., hydroxyethyl
methylcellulose having a weight average polymerization degree of
1000, a substitution degree of methoxyl groups of 1.8 and a molar
substitution of hydroxyethoxyl groups of 0.08 was obtained.
[0050] A ratio (A/B) of a molar fraction (A) of substituted
hydroxyethoxyl groups having hydroxyl groups of hydroxyethoxyl
groups substituted further with methoxyl groups to a molar fraction
(B) of unsubstituted hydroxyethoxyl groups having hydroxyl groups
of hydroxyethoxyl groups not substituted further with methoxyl
groups was found to be 0.9. The dissolution temperature and the
thermoreversible gel strength of the resulting hydroxyethyl
methylcellulose measured in the same manner as in Example 1 were
30.degree. C. and 150 g/cm.sup.2, respectively.
* * * * *